1. Field of the Invention
The present invention relates to a gear synchronizer mechanism adapted for use in manually shifted power transmissions, and more particularly, but not exclusively, to a gear synchronizer mechanism of the type which comprises a gear member provided at its one side with a cylindrical hub portion and rotatable on a transmission shaft, a hub member mounted on the shaft for rotation therewith, a clutch sleeve formed at its one side with an internal conical surface and at its inner periphery with internal spline teeth in continual engagement with external spline teeth of the hub member and being axially shiftable to be engaged at its internal spline teeth with external spline teeth of the cylindrical hub portion, a synchronizer ring formed at its outer periphery with an external conical surface for frictional engagement with the internal conical surface of the clutch sleeve and being axially movable on the cylindrical hub portion to effect synchronization between the shaft and the gear member when engaged at its external conical surface with the internal conical surface of the clutch sleeve in shifting operation, and resilient means for biasing the synchronizer ring toward clutch sleeve and for restricting axial movement of the synchronizer ring by engagement therewith in shifting operation.
2. Description of the Prior Art
In Japanese Patent Publication No. 51-48540, there has been proposed such a synchronizer mechanism as described above, wherein the synchronizer ring is formed at its inner periphery with a plurality of circumferentially equally spaced radial projections which are axially slidably disposed within corresponding radial grooves in the cylindrical hub portion of the gear member, and wherein a radially contractible annular spring is engaged with each recessed inner end of the radial projections to bias the synchronizer ring toward the clutch sleeve and engaged with an annular groove in the inner periphery of the cylindrical hub portion to restrict axial movement of the synchronizer ring. In shifting operation of the clutch sleeve, the synchronizer ring is engaged at its external conical surface with the internal conical surface of the clutch sleeve and urged toward the gear member under the thrust pressure applied thereto from the clutch sleeve. When the thrust pressure acting on the synchronizer ring exceeds a predetermined value, synchronization between the relative rotating parts is established, and the annular spring is disengaged from the annular groove of the cylindrical hub portion. Subsequently, the annular spring is radially inwardly compressed by engagement with an internal conical surface of the cylindrical hub portion.
In such arrangement of the annular spring as described above, reliable synchronization between the relative rotating parts may not be effected if the restriction force acting on the synchronizer ring is unstable due to an error in assembly of the components or differences in tolerances of the assembled components. In the case that an annular spring of large diameter cross-section is assembled as the annular spring to stabilize the restriction force acting on the synchronizer ring, it will cause an increase of frictional resistance when compressed by engagement with the internal conical surface of the hub portion and will cause an increase of the biasing force acting on the synchronizer ring in its shifted position. As a result, the biasing force of the spring will act to cause unexpected disengagement of the synchronizer ring from the clutch sleeve, and the internal conical surface of the hub portion will be defaced by frictional engagement with the spring in a short period of time.